A rear projection type display apparatus can comparatively easily realize large screen display in a reduced size and at a low cost in comparison with a direct sight type CRT, and therefore, its demand is increasing centering on North American markets. Particularly, unlike a rear projection type display apparatus using a CRT projection tube, highly fine display without any blur can be carried out to peripheral portions of a screen by dot matrix display, according to a rear projection type display apparatus having a projecting apparatus using a liquid crystal display element of a TN (Twisted Nematic) liquid crystal or the like as a two-dimensional optical switch element, and therefore, such a rear projection type display apparatus is expected as a prospective product of a high resolution digital television.
FIG. 11 is a schematic sectional view of a rear projection type display apparatus. A transmission type screen 703 is irradiated with a projected light beam 704 emitted from a projecting apparatus 701 via a mirror 702, and an image is displayed on a front face thereof.
As shown in FIG. 38, the transmission type screen 703 is normally constituted of a Fresnel lens sheet 1402 and a lenticular lens sheet 1401, and the Fresnel lens sheet 1402 is an optical part which operates similarly to a convex lens and functions of widening a suitable viewing range by bending a direction of a main light beam from the projecting apparatus 701 toward an observer.
The lenticular lens 1401 effectively distributes a limited projected light flux from the projecting apparatus 701 to an observing range of the observer to thereby provide a bright image as its object.
FIG. 36 is a schematic sectional view showing an example of a lenticular lens, and FIG. 37 is a schematic perspective view of the lenticular lens.
In the lenticular lens 1401, a plurality of cylindrical lenses 1501 are arrayed in one direction and black stripes 1502 are provided at portions other than portions for condensing a light beam, thereby restraining a contrast ratio with regard to an ambient light beam from lowering without any loss of the projected light beam ideally by disposing focal positions of the lenses 1501 on an observing face of a screen.
Generally, by arraying the lenticular lenses such that generators thereof are directed orthogonally to a display face, a wide viewing angle is provided in the horizontal direction. Therefore, a light beam is distributed in the vertical direction only by diffusion by a diffusing member blended in a base material of the lenticular lenses or surface portions thereof, and accordingly, a viewing angle in the vertical direction is considerably narrower than that in the horizontal direction. Further, according to the lenticular lens, lenses having a linear shape are regularly arranged, and therefore, moire interference fringe is liable to occur on the image.
In contrast thereto, Japanese Unexamined Patent Publication No. 2-77736 discloses a transmission type screen having a constitution in which a transparent base member 1601 is covered with spherical lenses 1602 which are fixed by a transparent resin, as shown in FIG. 39. According to the constitution, no die is used, and therefore, there is no restriction in size in view of fabrication and a seamless transmission type screen having a large screen can be realized. Further, a light beam incident from a side of the spherical lenses is converged by the lens effect of the spherical lenses and is diverged isotropically, and therefore, wide viewing angles are provided both in the horizontal and vertical directions.
Further, there is published a screen having a structure in which optical beads are fixedly attached on a transparent base member via a light-absorbing adhering agent layer and surfaces of the optical beads on the opposite side of the transparent base member are back-coated transparently in SID94 DIGEST pp. 741-744 (A Novel High-Resolution Ambient-Light-Rejecting Rear-Projection Screen).
Further, Japanese unexamined Patent Publication No. 9-318801 discloses a plane type lens having a structure in which very small spherical transparent beads are fixed on a transparent base member by a colored hot melt adhering agent layer and a transparent hot melt adhering agent layer. According to the structure, like Japanese Unexamined Patent Publication No. 2-77736, by the lens effect of the beads, there is provided isotropic viewing angles which are wide both in the horizontal and vertical directions. Further, an unnecessary light beam incident from outside is absorbed by a light-absorbing adhering agent layer (or colored hot melt adhering agent layer), and therefore, a high contrast ratio is provided even in a bright environment. Further, high resolution can be realized comparatively easily by reducing the diameter of the bead.
The above-described conventional plane type lens (hereinafter, referred to as a light distribution control element) is fabricated as follows: a flat polyethylene terephthalate (PET) resin film having a thickness of 120 μm is used as the transparent base member; a transparent adhering agent layer comprising a polyester-based hot melt adhering agent is formed in a thickness of 5 μm on a surface of the resin film; a colored adhering agent layer, in which the same polyester-based hot melt adhering agent is blended with 10 parts by weight of carbon black, is formed on the transparent adhering agent layer; and the entirety is solidified once.
Spherical transparent beads made of glass having a refractive index of 1.935 (wavelength: 589.3 nm) and a diameter of 50 μm are densely arranged to be dispersed on the entirety. While heating to soften the transparent adhering agent layer and the colored adhering agent layer in a thermostatic chamber, the transparent beads are pressed toward the transparent base member by a pressing plate, to thereby make the transparent beads embed in and fixedly adhere to the colored adhering agent layer and the transparent adhering agent layer. The thickness of the adhering layer after fixation is about 21 μm by adding those of the transparent adhering agent layer and the colored adhering agent layer, and the transparent beads are exposed from the adhering agent layer by about 58% of a diameter thereof.
When the fabricated light distribution control element is evaluated as a transmission type screen of a rear projection type display apparatus having a projecting apparatus using a TN type liquid crystal display element as a two-dimensional optical switch element (light bulb), there are provided wide viewing angles equal to or larger than 50 degree (in this case, an angle giving a brightness half of a front brightness) both in the horizontal direction and the vertical direction, and an unnecessary light beam incident from outside (an observer side) on the light distribution control element is absorbed by the colored adhering agent layer and black display at low brightness can be realized even under bright environment.
However, when an image projected on the light distribution control element is observed in an oblique direction, it is found that a fringe pattern substantially in shapes of concentric circles emerges and the image quality is significantly deteriorated. Further, it is also found that when observed in an oblique direction, a change in chromaticity unfavorable to the image is caused.
It is an object of the present invention to provide a light distribution control element without inducing any deterioration in image quality caused by occurrence of the above-described fringe pattern and a display apparatus having the high brightness, high contrast ratio and high viewing angle using the light distribution control element. Objects other than the above-described object will become apparent self-evidently from the following description.